The demand for wireless broadband is increasing and different solutions for meeting the demands are constantly presented. One solution is to increase the spectral efficiency of the communication network, which can be done by introducing the new radio access technology LTE (Long Term Evolution).
Another way to do this is to deploy more base stations and use smaller cells and the capacity of the system will be increased. However, the large amount of base stations also gives a high energy consumption which will be expensive and has a negative effect on the environment. Furthermore, the high bit rate of future wireless broadband needs a lot of signal processing in the base stations, and this will increase the energy consumption even more. Therefore there is a general need for reducing the energy consumption in the base stations.
Many small cells and dense deployment of base stations will probably also cause an increase of the co-channel interference between different cells. The co-channel interference will lead to deteriorated Signal to Interference plus Noise Ratio (SINR) and therefore lower bit rate for the customers.
One prior art solution for reducing the power consumption of a base station is called “Three sector omni”. This basically means that during low traffic scenarios a three sector base station turn off two out of three base bands, radios and power amplifiers and serves all three sectors with one baseband, radio and power amplifier. The radio chain in use is connected to the existing sector antennas at site such that an effective omni directional pattern is obtained. This type of solution is described in WO 2008/143567 A1.
Base stations often have three sectors, and each sector have its own base band, radio and power amplifier, se FIGS. 1a and 1b. A first sector antenna 101 covers the first sector, a second sector antenna 102 the second sector and a third sector antenna 103 the third sector. In transmit mode, Tx-mode, also called downlink mode, each antenna is connected to a Tx-chain (transmit chain) comprising means for a Tx-baseband 120 connected in series with means for a Tx-radio 110 and a power amplifier 100 with the power amplifier connected to the sector antenna. Each sector operates over a total frequency band ftot of the RBS. The majority of the power consumption is in the power amplifiers but also the means for Tx-base band and Tx-radio consume considerable power. Today, base stations run all three sectors all the time regardless of the amount of traffic load. This leads to unnecessary high power consumption due to that all means for Tx-base band and Tx-radio as well as power amplifiers for all sectors are running constantly.
When the Radio Base Station is operating in receive mode, Rx-mode, also called uplink mode, each sector antenna is also connected to an Rx-chain (receive chain) as illustrated in FIG. 1b. The Radio Base Station of FIG. 1b comprises three sectors with three Tx-chains and three Rx-chains. Each Tx-chain and each Rx-chain comprises an antenna end and a radio end, the antenna end is connected to one Tx/Rx-switch 130. Each Tx/Rx-switch is arranged to switch a sector antenna 101, 102, 103 to one Tx or one Rx-chain, the sector antenna being arranged to operate within a certain sector in space. Each Tx-chain comprises means for a Tx-base band 120 and a Tx-radio 110 as well as a power amplifier 100, PA, connected in series and with the power amplifier being connected to the Tx/Rx-switch 130. Each Rx-chain comprises means for an Rx-base band 160 and an Rx-radio 150 as well as a low noise amplifier 140, LNA, connected in series and with the low noise amplifier being connected to the Tx/Rx-switch 130. Each Tx-chain is arranged to operate within a total transmit frequency band ftx and each Rx-chain is arranged to operate within a total receive frequency band frx. The switching between Rx and Tx-mode in a sector is performed with the Tx/Rx-switch 130 which can be realized as a duplexer or a circulator.
FIG. 2 illustrates an energy saving solution called “Three sector omni”. In “Three sector omni” a switch network 204 has been placed between the sector antennas, 101-103, and the power amplifiers. For low traffic scenarios the switch network can be configured so that one Tx-base band 120, one Tx-radio 110 and one power amplifier 100 serves all three sectors. The remaining Tx-base bands, Tx-radios and power amplifiers could then be turned off in order to reduce the power consumption. The whole frequency band, ftx, will still be used in each sector. This lead to that the gain of the radiation pattern from the sector antennas of the site will be reduced 5 dB compared to the prior art solution shown in FIG. 1a. This will have a negative impact on the capacity and coverage of the site.
The prior art solutions described above can also be used in Rx-mode. The power consumption in receive mode is substantially less than in transmit mode but it is of course also desirable to reduce power consumption in the receive mode.
The problem with prior art solutions has been exemplified with a three sector Radio Base Station. The problem is however in general applicable to nodes in communication systems such as different types of Radio Base stations in wireless communication systems.
There is thus a need for an improved node with a possibility for reduced power consumption at low traffic load, especially in transmit mode, without having a negative impact on the total capacity and coverage.